Studies which were initiated last year on the characterization of a new member of the polyomavirus genus, a B-lymphotropic papovavirus (LPV) have been expanded during this past year to include biochemical studies on the viral proteins as well as its DNA. Three viral polypeptides have been identified, both in purified virus preparations as well as in infected cells. These are the major capsid proteins, VP-1 (41K), and two internal proteins, VP-2 (35K) and VP-3 (26K). Besides the structural proteins, an early, virus-coded 81K protein was identified in infected cells. The 81K protein may be the large T-antigen of LPV. Investigations on the genome of LPV is proceeding along two different directions. A more detailed physical map is being constructed and, in addition, studies are underway to compare the LPV DNA with the genomes of the other primate polyomaviruses, BK, JC, and SV40. In biological studies, the prevalence of antibody to LPV in humans has been expanded. We have previously reported that about 25-30 percent of adults have antibody to LPV. Only 5 percent of people under 20 year have been found to be positive for antibody to LPV. Infection therefore appears to occur later in life in humans. Attempts to transform a variety of human and rodent cvells with LPOV have been unsuccessful, but these experimets are still continuing.